1. Field of the Invention
This invention relates to an electronic device such as a one-chip microcomputer for controlling an electronic equipment, which is suitable installation in the electronic equipment.
2. Description of the Related Art
In an electronic equipment, such as a commercially-used video tape recorder (VTR) integral with a camera (hereinafter referred to as "camera-integrated VTR"), a compact video deck or the like, a one-chip microcomputer has an integrated structure including a central processing unit (CPU) for performing access control for a storage means and calculation processing. The one-chip microcomputer further includes a storage means, such as a read only memory (ROM), for fixedly storing information. The one-chip micro-computer further includes a random access memory (RAM) through which performing information write-in and read-out operations can be carried out. The one-chip microcomputer further includes a peripheral circuit such as an input/out port, etc. This one-chip microcomputer has been conventionally used in a state where it is installed in the main body of the electronic equipment as described above.
Such one-chip integrated electronic devices have the potential to be low in cost due to mass production thereof. In addition, the amount of programs which can be stored in a ROM have been remarkably increased, particularly owing to the recent development of a semiconductor integration technique, so that various kinds of complicated control contents can be performed in accordance with the programs stored in the ROM.
As described above, various kinds of complicated controls can be performed in recently-developed electronic equipment by storing a large amount of programs into a ROM. However, the increased amount of programs stored into the ROM increases the chances of inducing a bug in the ROM. Particularly in the case where a bug is found after products have been mass-produced, the following countermeasures have been conventionally adopted. That is, those microcomputers which are mass-produced so that the bug is corrected are exchanged for those microcomputers having the bug which have been installed in electronic equipments. Alternatively, external parts for correcting the bug are newly equipped to electronic equipments having the bug. However, such countermeasures have caused the cost of the products to be increased. Further, an electronic equipment such as a camera-integrated VTR which has high packaging density of parts has a problem that the countermeasure of newly equipping an external part is very difficult.